EP0559060A1 - Structure type Dodekasil 1 H chathrasil with small average crystal size - Google Patents

Abstract

The invention relates to a process for preparing crystalline clathrasil of the dodecasil 1 H structure type having a mean crystal size of no more than 20 mu m, characterised in that an alkaline aqueous silicate-containing medium which contains templates and crystallisation nuclei is tempered, the crystallisation nuclei content based on the SiO2 content of the medium being not less than 1% by weight.

Description

The invention relates to a clathrasil of the structure type Dodekasil 1 H with a small average particle size and platelet-shaped pigments based on such particles and corresponding production processes.

beschrieben werden können, worin A ein Kation mit der Ladung y, T ein trivalentes Kation, welches tetrahedral durch 4 O-Atome koordiniert ist, z die Anzahl zusäzlicher O-Atome zur Kompensation von Gitterunterbrechungen, AX Ionenpaare und M Gastpartikel sind und u, v und w 0, 1, 2, ... bedeuten. Als Kationen A kommen z.B. Alkali- oder Erdalkaliionen in Frage, T kann z.B. ein Aluminium- oder Borkation sein, und für X kommt eine Vielzahl von Anionen wie z.B. OH, Halogen etc. in Frage. Die Gastpartikel, welche auch als Template bezeichnet werden, werden in die Hohlräume der Porosilstruktur eingelagert und beeinflussen daher bei der Synthese der Porosile ganz wesentlich deren Struktur. Bei den Gastpartikeln handelt es sich i.a. um neutrale Moleküle, aber insbesondere bei geladenenen Porosilstrukturen können manchmal auch geladene Gastpartikel eingelagert werden. In diesem Fall muß die obige Formel (1) entsprechend abgeändert werden.Clathrasile belong to the class of porous tectosilicates or Porosile, which according to H. Gies and B. Marler, Zeolites, 12 (1992), 42 by the general formula

can be described in which A is a cation with the charge y, T is a trivalent cation which is tetrahedral coordinated by 4 O atoms, z is the number of additional O atoms to compensate for lattice interruptions, AX ion pairs and M guest particles and u, v and w mean 0, 1, 2, .... Cations A include, for example, alkali or alkaline earth ions, T can be, for example, an aluminum or boron cation, and X can be a variety of anions such as OH, halogen, etc. The guest particles, which are also used as templates are embedded in the cavities of the porosil structure and therefore have a significant influence on their structure during the synthesis of the porosil. The guest particles are generally neutral molecules, but in particular with charged porosil structures, charged guest particles can sometimes also be embedded. In this case, the above formula (1) must be modified accordingly.

Porosile is divided into clathrasile and zeosile according to the size and shape of the cavities. While zeosiles have cage-like or channel-like pores that are so large that the template molecules are expelled from the pores under relatively mild conditions and may be exchanged for other guest molecules, clathrasils have very small cage-like cavities, the openings of which are too small to be that an enclosed molecule could leave the pore system. Of particular interest are clathrasils of the Dodecasil 1 H type, which have a platelet-shaped, hexagonal structure.

The clathrasils have hitherto been prepared by hydrothermal crystallization at, for example, 200 ° C. from a silicate-containing solution to which template molecules such as, for example, adamantylamine are added. However, this production process produces crystals with an average size of typically 150-500 μm. Such large crystals are, however, not suitable for incorporation into lacquer formulations, coatings etc. and, moreover, they are extremely sensitive to breakage. In addition, in the conventional synthetic processes such template molecules are usually used in excess whose dimensions correspond as closely as possible to the cavity dimensions in the Dodekasil 1 H; Examples include: 1-adamantylamine, piperidine or azabicyclononanium iodide. However, the materials listed are relatively expensive and unsuitable for economical, large-scale pigment production.

There was therefore a need for clathrasils of the Dodekasil 1 H structure type with a small average crystal size of less than about 20 μm and for a corresponding economical and large-scale production process.

The present invention was based on the object of providing clathrasils of the 1 H structure type and a process for their preparation, which in any case meet the stated requirements better than conventional clathrasils of the Dodekasil 1 H structure type and conventional production processes. Other objects of the present invention will be apparent to those skilled in the art from the detailed description that follows.

It has been found that these objects can be achieved by providing the process according to the invention and the dodekasil 1 H-clathrasils according to the invention.

The invention thus relates to a process for the production of crystalline clathrasil of the structure type Dodekasil 1 H with an average crystal size of not more than 20 μm. characterized in that an alkaline aqueous silicate-containing medium containing crystallization nuclei and template molecules is annealed, the content of crystallization nuclei based on the SiO₂ content of the medium being not less than 1% by weight.

The invention furthermore relates to dodekasil 1-clathrasils with an average crystal size of not more than 20 μm and platelet-shaped pigments based on such dodekasil 1 H-clathrasils.

In the process according to the invention, one or more templates and crystallization nuclei are added to the reaction mixture, which is based on an alkaline aqueous silicate-containing medium.

Small-scale dodecasil in particular are used as crystallization nuclei 1 H-clathrasil crystals are used, which have been obtained, for example, by conventional manufacturing processes and may already contain templates. The Dodekasil 1 H-clathrasil crystals can be ground, for example, in a vibratory mill, and the average particle size of the crystallization nuclei obtained is typically between 0.2 and 1.5 μm and in particular about 1 μm.

It has now been found that the size of the dodekasil 1 H-clathrasil crystals obtained can be influenced in a targeted manner by the added amount of seed crystals or crystallization nuclei. While with relatively small amounts of seed crystals around 1 to 10% by weight and in particular 5 to 10% by weight dodekasil 1 H-clathrasil crystals with an average particle size between 5 and 15 µm are obtained, at higher seed crystal concentrations of more than 10% by weight and in particular between 10 and 20% by weight of smaller crystals with an average particle size of typically less than 5 μm.

These Dodekasil 1 H clathrasil crystals are hexagonal platelets with an average thickness between typically 0.2 and 2 µm; the ratio of lateral extent and thickness of these dodecasil 1 H-clathrasil crystals, referred to as aspect ratio, is therefore typically between 1 and 100 and in particular between 10 and 100.

Template molecules are also added to the reaction batch, the template content of the reaction batch based on the SiO 2 mol number typically being between 0.03 and 2 and in particular between 0.05 and 1.5. If the template content is chosen to be less than 3 mol%, dodekasil 1 H-clathrasil crystals, which are often very strongly overgrown, are obtained, which in many cases cannot be separated by grinding without the Dodekasil 1 H platelets being destroyed; these very overgrown dodekasil 1 H-clathrasils are therefore generally unsuitable for pigment production. The template content is particularly preferably higher than 10 mol%, based on the SiO₂ mol number of the reaction mixture.

Increasing the template concentrations to more than 100 mol% generally does not improve the morphology of the Dodekasil 1 H-clathrasil platelets and will therefore generally not be used for economic reasons.

Surprisingly, it was found that, in contrast to the conventional Dodekasil 1 H-clathrasil synthesis, the choice of the template is much less critical. For example, simple amines such as Hexamethylene diamine, simple quaternary ammonium compounds such as Triethyl methyl ammonium bromide, surfactants such as e.g. Sodium dodecyl sulfate and simple alcohols can also be used. This list is only intended to illustrate the invention and in no way limit it; a large number of other molecules can also be used as template molecules. It is crucial that the requirements for the geometry of the template molecules in the production process according to the invention are substantially lower than in conventional processes. In the method according to the invention, the dodekasil 1 H-clathrasil structure is apparently essentially induced by the seed crystals, the template molecules having a supporting effect. In contrast, the structure in conventional syntheses is only induced and controlled by the template molecules, and it is understandable that the template molecule must specify the desired geometric structure as precisely as possible.

When using geometrically inaccurate templates, it is sometimes observed that the dodekasil 1 H platelets obtained have grown together. However, these deviations from perfect morphology are usually only relatively small, and the reaction products obtained can generally be prepared by ultrasound treatment without destroying the Dodekasil 1 H platelets.

• * daß durch die Variation der Konzentration der zugesetzten Kristallisationskeime die mittlere Größe der erhaltenen Dodekasil 1 H-Clathrasilkristalle gezielt beeinflußt werden kann und
• * daß durch den Zusatz von Kristallisationskeimen die Wahl der Templatmoleküle wesentlich unkritischer wird.

The use of crystallization nuclei for the synthesis of zeolites is known (see DE 29 35 123, for example), but the synthesis of dodekasil is 1 H-clathrasil with the addition of crystallization nuclei not described in the prior art and, in particular, has not hitherto been recognized,

• * that the mean size of the dodekasil 1 H-clathrasil crystals obtained can be influenced in a targeted manner by varying the concentration of the added crystallization nuclei and
• * that the addition of crystallization nuclei makes the choice of template molecules much less critical.

The last point makes an industrial and economical synthesis of dodekasil 1 H-clathrasil crystals possible in the first place.

The alkaline aqueous medium typically has an NH₃ content of 15 to 45 mol, which corresponds to the same OH content with complete dissociation of the base and an H₂O content of 40-70 mol, based on the SiO₂ mol number of the medium. To adjust the required OH content or the corresponding pH, a base, usually NH₃ is added; the pH of the alkaline aqueous medium is preferably between 12 and 13. The ranges given for OH content, H₂O content and pH are generally. preferred, although deviations from these areas upwards and downwards are also possible.

In particular, silica can be used as the source of silicate, but aqueous solutions of alkali silicates or aluminosilicates or other sources of silicate are also possible.

The alkaline-aqueous silicate-containing medium characterized in more detail above is then subjected to an annealing treatment, whereby the clathrasil crystals are obtained. The heating rate is preferably between 0.05 and 50 K / min and in particular between 0.1 and 20 K / min, and the final temperature is preferably chosen between 400 and 470 K and in particular between 423 and 453 K. The temperature can be ramped up more or less linearly, or it can be more complicated Temperature programs in which the temperature is kept constant at one or more intermediate values for a while, for example, before it is then ramped up, or other temperature programs are used.

The selection of a suitable temperature program is based on the idea that the clathrasil synthesis can be roughly divided into two phases, namely the nucleation as the first phase and the addition of monomers to a species capable of growth as the second phase. For example, when using a small or relatively small seed crystal concentration, a relatively low heating rate and the use of temperature ramps are often preferred, while heating is often faster at higher seed crystal concentrations. Furthermore, Dodekasil 1 H-clathrasil crystals of particularly perfect morphology are often obtained at low heating rates.

The person skilled in the art can easily adapt the heating-up rate and heating-up program to the composition of the alkaline-aqueous silk-containing medium used and optimize it with regard to the desired crystal morphology and yield, without any inventive step. The total annealing time is preferably between 3 and 10 days, the medium being kept at the final temperature preferably between 3 and 10 days.

The platelet-shaped dodekasil 1 H-clathrasil crystals produced by the process according to the invention can be used for the production of platelet-shaped effect pigments. For this purpose, the crystal platelets are suspended in an aqueous medium and wet-chemically coated with one or more compact smooth layers of highly refractive metal oxides such as TiO₂, ZrO₂, ZnO, iron oxide, chromium oxide by methods such as those described in German patents and patent applications 14 67 468, 19 59 998, 20 09 566, 22 14 545, 22 15 191, 22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 354, 31 51 355, 32 11 602 and 32 35 017 are listed. The cavity openings of the Dodekasil 1 H structure are 0.28 nm or less and are therefore so small that they are practically not noticed by the deposited metal hydroxides or metal oxyhydroxides. Because of the significantly lower aspect ratio of such pigments compared to, for example, mica pigments, the pearlescent effect is less pronounced in the pigments according to the invention, and the pigments according to the invention can more appropriately be referred to as shimmering absorption pigments.

It was also found that the Dodekasil 1 H-clathrasil crystals are excellently suitable as carriers for organic colorants. For this purpose, organic colorants such as e.g. Methylene blue, methyl orange, bromocresol purple, malachite green or phenol red added, this list is only intended to illustrate and not limit the invention. The colorant molecules may only be chosen so large that they no longer fit into the cavities of the Dodekasil 1 H clathrasil. In Dodekasil 1 H there are two types of cavities with a cavity opening of 0.28 nm, namely icosahedra and dodecahedron cages, which have an inner diameter of 1.12 nm. There is also another type of dodecahedron cage with an even smaller cavity opening consisting of a SiO five-membered ring, which have an inner diameter of 0.57 nm. The person skilled in the art can easily choose organic colorants that can be stored on the basis of the cage geometry given.

During the synthesis, the colorant molecules are embedded in particular in the first-mentioned icosahedron and dodecahedron cavities with a cavity opening of 0.28 nm; the smaller dodecahedron cages, on the other hand, often remain vacant. The narrow cavity openings of only 0.28 nm ensure that the colorant molecules can practically not get out of the cavities, so that the resulting inclusion pigments are extremely colourfast and non-bleeding. They are also beyond neatly stable against oxidants, since the narrow cavity openings cannot be passed through by O atoms.

Since the template molecules and the colorant molecules compete for the cage sites in the synthesis, the concentration of the template molecules is generally chosen very low. The colorant molecules often also act as structure-inducing templates, so that only a very low template concentration or no additional templating at all is required. The quotient of the amount of template and colorant molecule additive is preferably between 0 and 0.5 and in particular between 0 and 0.2.

The color can also be achieved by the targeted calcination of crystals loaded with non-colored molecules. Due to the directing effect of the cavity system, relatively defined pyrolysis products are formed, which have different colors depending on the pyrolysis temperature. In this way, yellow, red, green and brown shades could be achieved.

The examples described below are intended to illustrate the invention without limiting it.

example 1

0.8 g of fumed silica with the composition SiO₂ were mixed with 0.04 g of finely ground dodecasil 1 H-clathrasil crystals, which served as seed crystals and are referred to below as SiO₂ (seed crystals), 0.4 g of 1-adamantylamine and 23.4 ml of 32% by weight ammonia at room temperature Stirred for 1 min.

The reaction mixture had the following molar composition:
1 SiO₂: 0.05 SiO₂ (seed crystals): 0.2 1-adamantylamine: 60 H₂O: 29 NH₃
With a heating rate of 0.5 K / min and a final temperature of 453 K, perfect Dodekasil 1 H clathrasil crystals with an average size of 8 ± 2 µm were obtained after 144 hours.

Example 2

0.8 g of fumed silica with the composition SiO₂ were 0.12 g of finely ground dodecasil 1 H-clathrasil crystals, which served as seed crystals and are referred to below as SiO₂ (seed crystals), 0.4 g of 1-adamantylamine and 23.4 ml of 32% by weight ammonia at room temperature for 1 min.

The reaction mixture had the following molar composition:
1 SiO₂: 0.15 SiO₂ (seed crystals): 0.2 1-adamantylamine: 60 H₂O: 29 NH₃
With a heating rate of 0.5 K / min and a final temperature of 453 K, perfect Dodekasil 1 H-clathrasil crystals with an average size of 4 ± 1 µm were obtained after 144 hours.

Example 3

• a) 0.8 g of fumed silica of the composition SiO₂, 1.47 g of 1-adamantylamine
  and 23.4 ml of 32% by weight ammonia at room temperature for 1 min.
  The reaction mixture had the following molar composition:
  1 SiO₂: 0.73 1-adamantylamine: 60 H₂O: 29 NH₃
  With a heating rate of 0.5 K / min and a final temperature of 453 K, perfect Dodekasil 1 H-clathrasil crystals were obtained after 144 hours, which were ground in a vibratory mill, the average particle size being between 0.2 and 1.5 µm.
• b) 0.8 g of pyrogenic silica of the composition SiO₂ were 0.08 g
  finely ground Dodekasil 1 H-clathrasil crystals from the Adamantylansatz according to Example 3 a), which served as seed crystals and are hereinafter referred to as SiO₂ (seed crystals), 1.2 g triethylammonium bromide and 23.4 ml of 32% by weight ammonia at room temperature for 1 min.
  The reaction mixture had the following molar composition:
  1 SiO₂: 0.1 SiO₂ (seed crystals): 0.5 TEAMBr: 60 H₂O: 29 NH₃
  At a heating rate of 0.5 K / min and a final temperature of 453 K, dodekasil 1 H-clathrasil crystals with an average size between 5 and 10 µm were grown after 144 hours.

Example 4

0.8 g of pyrogenic silica with the composition SiO₂ were mixed with 0.08 g of finely ground dodecasil 1 H-clathrasil crystals (from an adamantyl batch according to Example 3 a), which served as seed crystals and are hereinafter referred to as SiO₂ (seed crystals), 4 g of sodium dodecyl sulfate and 23.4 ml of 32% by weight % ammonia stirred at room temperature for 1 min.

The reaction mixture had the following molar composition:
1 SiO₂: 0.1 SiO₂ (seed crystals): 1.0 Na-DDS: 60 H₂O: 29 NH₃
At a heating rate of 0.5 K / min and a final temperature of 453 K, dodekasil 1 H-clathrasil crystals with an average size between 5 and 10 µm were grown after 144 hours.

Example 5

0.8 g of pyrogenic silica of the composition SiO₂ were with 0.08 g of finely ground dodecasil 1 H-clathrasil crystals (from an adamantyl batch according to Example 3 a), which served as seed crystals and hereinafter referred to as SiO₂ (seed crystals) , 0.3 g of 1-adamantylamine and 23.4 ml of 32% by weight ammonia are stirred at room temperature for 1 min.
The reaction mixture had the following molar composition: 1 SiO₂: 0.1 SiO₂ (seed crystals): 0.4 1-adamantylamine: 60 H₂O: 29 NH₃

At a heating rate of 0.5 K / min and a final temperature of 453 K, dodekasil 1 H-clathrasil crystals with an average size between 5 and 10 µm were grown after 144 hours.

A corresponding approach without the addition of seed crystals
1 SiO₂: 0.4 1-adamantylamine: 60 H₂O: 29 NH₃
led to a complete conversion at a heating rate of 0.5 K / min and a final temperature of 453 K only after a reaction time of 240 hours, with overgrown dodekasil 1 H-clathrasil crystals having an average size between 180 and 270 μm being obtained.

Example 6

0.8 g of fumed silica of the composition SiO₂ were stirred at room temperature for 1 min with 1.4 g of 1-adamantylamine and 23.4 ml of 32% ammonia. The reaction mixture had the following molar composition:
1 SiO₂ x 0.7 1-adamantylamine x 60 H₂O x 29 NH₃
With a heating rate of 0.5 K / min and a final temperature of 453K, perfect Dodecasil 1H clathrasil crystals with an average size of 200 µm were obtained after 144 hours. The crystals are heated at 10K / min to the respective pyrolysis temperature for 30 min. The results are shown in the following table: Pyrolysis temperature [K] colour 773 colorless 873 red 1023 green 1173 brown > 1273 black

Claims (11)

Process for the preparation of crystalline clathrasil of the structure type Dodekasil 1 H with an average crystal size of not more than 20 µm, characterized in that an alkaline aqueous silicate-containing medium containing template and crystallization nuclei is annealed, the on the SiO₂ content of the medium related content of crystallization nuclei is not less than 1% by weight. A method according to claim 1, characterized in that dodecasil 1 H-of the clathrasil crystals H are used as the crystallization nuclei. Method according to one of claims 1 or 2, characterized in that quaternary ammonium compounds, amines, surfactants and / or alcohols are used as templates. Method according to one of claims 1-3, characterized in that the medium additionally contains colorants which are incorporated into the clathrate structure. A method according to claim 4, characterized in that the medium contains organic colorants. Process according to Claim 5, characterized in that the organic colorant is methylene blue, methyl orange, bromocresol purple, malachite green or phenol red. Process according to claims 1-6, characterized in that the medium has an NH₃ content of 15 to 45 and an H₂O content of 40 to 70, each based on the SiO₂ mole number. Process according to claims 1-7, characterized in that the medium is heated up to a final temperature at an essentially linear heating rate, the heating rate being between 0.1 and 20 K / min and the final temperature between 400 and 480 K. Platelet-shaped, crystalline clathrasil of the structure type Dodekasil 1 H, characterized by an average crystal size of not more than 20 µm. Platelet-shaped pigment based on a clathrasil according to claim 9, which contains embedded colorants and optionally additionally coated with one or more metal oxide layers. Use of the pigments according to claim 11 for pigmenting plastics, paints and cosmetics.